Science

Mount Hood is one of the most seismically active volcanoes in the Washington and Oregon Cascades, and the most seismically active volcano in Oregon. In an average month 1-2 earthquakes are located within 5 km (3 miles) of the summit. Earthquakes large enough to be felt occur on Mount Hood every two years on average. Seismic monitoring, in effect since 1977, indicates a generalized concentration of...

Debris flows ( lahars) pose the greatest hazard to people near Mount Rainier. A debris flow is a mixture of mud and rock debris that looks and behaves like flowing concrete. Giant debris flows sometimes develop when large masses of weak, water-saturated rock slide from the volcano's flanks. Many of these debris flows cannot be predicted and may even occur independently of a volcanic eruption...

Eruptions of Mount Rainier usually produce much less volcanic ash than do eruptions at Mount St. Helens. However, owing to the volcano's great height and widespread cover of snow and glacier ice, eruption triggered debris flows ( lahars) at Mount Rainier are likely to be much larger--and will travel a greater distance--than those at Mount St. Helens in 1980. Furthermore, areas at risk from debris...